1. Field of the Invention
The present invention relates to a magnetically levitated motor that magnetically, rotationally supports a rotor in a non-contact manner.
2. Description of Related Art
Conventionally, magnetic bearings that support a rotary body in a non-contact matter are used in various fields. In recent years in particular, radial magnetically levitated motors that integrate a function as a magnetic bearing and a function as a motor have been proposed. A magnetically levitated motor has an advantage in that torque generation for a rotor and positional control of a rotor shaft can be simultaneously performed.
For example, a conventional magnetically levitated motor is equipped with a stator having magnetic poles formed on its inner circumferential surface in which each of the poles is wound with a single-pole winding, a rotor having M number of magnetic poles that are composed of permanent magnets and confronted with the inner circumferential surface of the stator with a gap provided between them, and a control device that conducts current in the windings of the stator for generating a rotary magnetic field with Mxc2x12 number of poles along the inner circumferential surface of the stator and for rotating the rotor. Levitation force is obtained by mutual magnetic actions between the rotary magnetic field of the Mxc2x12 number of poles generated along the internal surface and the permanent magnets of the rotor. Current to rotate the rotor that is conducted through the windings of the stator is superposed over the current to obtain the levitation force, such that the rotor is magnetically levitated and rotationally driven.
However, the conventional magnetically levitated motor described above requires a complex magnetic flux distribution for the stator, which results in a complex structure, and complex levitation force control is required. Accordingly, it is difficult for the motor to increase the motor speed, and there is a problem in that the levitation force is weak and therefore its efficiency is unsatisfactory.
In view of the above, it is an object of the present invention to provide a magnetically levitated motor having a stator with a simplified structure, which only requires a simplified control that avoids one of the magnetic levitation force control and the rotational torque control from affecting the other. It is also an object of the present invention to provide an efficient magnetically levitated motor that optimally accommodates very high-speed rotations.
In accordance with one embodiment of the present invention, a magnetically levitated motor may comprise a stator having windings for rotation and windings for levitation, and a rotor having a rotor magnet magnetized in multiple poles, the stator and the rotor being disposed opposite to each other, wherein a rotary shaft of the rotor is levitated in a direction orthogonal to an axis of the rotor and rotationally driven by magnetic force, wherein the rotor magnet includes four magnetic poles provided adjacent to one another in a rotational direction at intervals of 90 degrees, and each of the windings for rotation and the windings for levitation has concentrated windings spaced at intervals of 30 degrees in a rotational direction to provide induction conductive winding sections at twelve locations. In one aspect of the present invention, each two of the induction conductive winding sections spaced at an interval of 90 degrees among the induction conductive winding sections at twelve locations are connected to form one winding set such that six winding sets are formed in total in each of the windings for rotation and the windings for levitation, and current for rotation and current for levitation are conducted through the respective six winding sets to perform rotation and levitation of the rotor. As a result, substantially perfect levitation and rotation can be achieved.
Moreover, separations between the induction conductive winding sections in the winding sets, which respectively correspond to going paths and returning paths in windings, are set at intervals of 90 degrees, which correspond to the separations of the rotor magnets. Therefore, its driving frequency is reduced by half, compared to, for example, a magnetically levitated motor with a rotor magnet having eight magnetic poles and a winding having six poles. As a result, in accordance with the present embodiment, a driving amplifier with a greater speed is not necessary, and heat generation and lowered efficiency that may be caused by an increase in iron loss can be effectively prevented.
In accordance with another embodiment of the present invention, stators and rotor may be formed in a planar confronting configuration, and two planar rotor magnets may be arranged in a direction of a rotor axis of the rotor. The stators may be disposed on both sides of the two planar rotor magnets to be interposed by the stators, and a winding for rotation and a winding for levitation may be mounted on each of the stators. As a result, greater levitation force and rotational torque are obtained, and controls of space four axes except the positional control in the rotational axis direction can be performed.
Furthermore, in accordance with still another embodiment of the present invention, a magnetically levitated motor may be formed in a cylindrical-confronting configuration, and a pair of stator-rotor sets in the cylindrical-confronting configuration may be arranged in a direction of the rotational axis. The motor having this configuration is also capable of producing greater levitation force and rotational torque, and performing controls of space four axes except the position control in the rotational axis direction.
Other objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.